The telephone subscriber stations in general include components for signaling an incoming call, for indicating the busy or idle condition of the station, for directing destinations, as well as for communication with other subscriber stations. Among the components used to facilitate the communication between connected subscriber stations are inductive elements, such as transformers. These inductive elements, besides being costly, are also cumbersome, especially in comparison with modern solid state circuitry. Another fault with the cumbersome, inductive components is that they are not amenable to hybridization.
The inductive elements are used for matching the load of subscriber station networks. The load includes the telephone lines coupling the subscriber stations to the central office. The characteristics of the lines can vary depending upon such variables as ambient climatic conditions. Networks using inductive components are used to match the substation to an average line length and ambient condition. The inductive components are not readily variable, because of cost and physical condition. Thus, the average substation is not properly matched to the telephone line.
The condition of the substation that is not properly matched, which causes the most difficulties, is, of course, where the transmission and reception of communication signals is overly attenuated. With the solvent of solid state electronics, it is easier to equip the substation with amplifiers to aid in overcoming the impedance matching problems. This, of course, is an expensive way of doing things, so that the cost effectiveness of the system rapidly deteriorates.
Accordingly, an object of the present invention is to provide new and unique electronic subscriber station networks.
Yet another object of the present invention is to provide solid state networks for subscriber stations which transmit and receive signals which are almost constant independently of variations in the line length.
Still another object of the present invention is to provide amplification both for the transmitter and receiver in the subscriber handset.
Yet another related object of the present invention is to use the same circuitry which makes the subscriber station network independent of variations in line impedance for controlling the amplitude of the side tone.
Still another object of the present invention is to provide electronic network circuits which limit the current going through the transmitter, thereby preventing its overload. The current limiting, which is inherently provided by the electronic circuit network used for controlling load matching and side tone, also eliminates the need for transmitter overload protection.
Still another object of the present invention is to provide solid state telephone networks which eliminate inductive components and are accordingly readily amenable to hybridization.